Alum.—In some towns alum is added to the boiling water in which straw is treated. It is usually employed in combination with other bleaching agents.
Dyes Used on Mat Straws.
Mordants.
A mordant is a substance employed to fix the dye to the material. In general, different ones are needed for different dyes and various materials. In some cases the mordant is added to the dye liquid; in others the material is previously treated with it before being colored. The most important are the mineral mordants, such as the alumina, the iron, the tin, and the chrome. These are not used in the Philippines with local vegetable dyes. Tannin is also important and is employed to some extent in the Philippines, being generally obtained from the mangrove tan barks. Wood ashes are little used but vinegar and lemon juice are important.
Kolis.—The leaves of this plant (Memecylon edule) are commonly used in mordanting buri straw before dyeing it with sappan wood. In Tanay, Rizal, it is employed on sabutan straw with all of the vegetable dyes. It is known as guisian (Laguna), duigim (Ilocos, Pangasinan), kulis (Rizal, Nueva Ecija, Bataan), tagobachi (Leyte), kasigay (Ilocos Norte), agam (Negrito, Cagayan), guisoc-guisoc (Sorsogon), macaasin (Tayabas), baian (Zambales), diyatdiyatan (Tayabas), candong (Pangasinan), dioc (Pangasinan).
Natural Vegetable Dyes.
Numerous natural vegetable dyes are employed in the Philippines. Those used on the mat straws are limited in number. The important ones only are here noted. The whole question of dyes is a most difficult one and hardly warrants the time which has been spent upon investigating the various dye materials, nor the effort which would be necessary to determine definitely the methods by which they can be used on mat straws. The artificial dyes have driven the natural vegetable dyes out of use because they are cheaper and are more easily applied, and because in most cases they produce more pleasing and lasting colors.